Alternator under-frequency detecting circuit

ABSTRACT

An alternator under-frequency detecting circuit for reducing the alternator output potential with conditions of less than normal output potential frequency. A source of each an alternating current sensing potential and an alternating current auxiliary sensing potential are connected in series aiding relationship across the alternating current input circuitry of a sensing potential rectifier circuit and a pair of silicon-controlled rectifiers are connected in an opposite polarity relationship across the source of alternating current auxiliary sensing potential. A trigger signal, produced at the beginning of each selected half-cycle of the alternating current auxiliary sensing potential for a predetermined duration of time greater than the normal frequency period of the selected half-cycles is applied across the gate-cathode electrodes of one of the siliconcontrolled rectifiers. With normal alternator output potential frequency, the silicon-controlled rectifiers are triggered conductive to effectively shunt the auxiliary sensing potential from the rectifier circuit and the alternator-rectifier system functions normally. With less than normal alternator output potential frequency, the silicon-controlled rectifiers are not triggered conductive, consequently, the sensing and auxiliary sensing potentials are applied across the rectifier circuit in a series aiding relationship, are rectified thereby and sensed by a potential regulator circuit which decreases the alternator field excitation and output potential magnitude.

United States Patent [72] Inventor Richard N. Lehnhofi Dayton, Ohio45439 [21] Appl. No. 90,623 [22] Filed Nov. 18, 1970 [45] Patented Nov.2, 1971 [73] Assignee General Motors Corporation,

Detroit, Mich.

[54] ALTERNATOR UNDER-FREQUENCY DETECTING CIRCUIT 5 Claims, 1 DrawingFig.

[52] US. Cl 322/24, 321/18, 322/28, 322/32, 322/59, 323/24, 323/45 [51]Int. Cl 1102p 9/26, H02p 9/42 [50] Field of Search 322/24, 28, 29, 32,59; 321/18; 323/22 SC, 24, 45

[56] References Cited UNITED STATES PATENTS 3,113,259 12/1963 Walker323/45 3,389,326 6/1968 l-lyvarinen 322/28 3,521,148 7/1970 Kirk et a1.322/28 Primary ExaminerGerald Goldberg Attorneys-Eugene W. Christen,Creighton R. Meland and Richard G. Stahr ABSTRACT: An alternatorunder-frequency detecting circuit for reducing the alternator outputpotential with conditions of less than normal output potentialfrequency. A source of each an alternating current sensing potential andan alternating current auxiliary sensing potential are connected inseries aiding relationship across the alternating current inputcircuitry of a sensing potential rectifier circuit and a pair ofsilicon-controlled rectifiers are connected in an opposite polarityrelationship across the source of alternating current auxiliary sensingpotential. A trigger signal, produced at the beginning of each selectedhalf-cycle of the alternating current auxiliary sensing potential for apredetermined duration of time greater than the normal frequency periodof the selected half-cycles is applied across the gate-cathodeelectrodes of one of the silicon-controlled rectifiers. With normalalternator output potential frequency, the silicon-controlled rectifiersare triggered conductive to effectively shunt the auxiliary sensingpotential from the rectifier circuit and the alternator-rectifier systemfunctions normally. With less than normal alternator output potentialfrequency, the silicon-controlled rectifiers are not triggeredconductive, consequently, the sensing and auxiliary sensing potentialsare applied across the rectifier circuit in a series aidingrelationship, are rectified thereby and sensed by a potential regulatorcircuit which decreases the alternator field excitation and outputpotential magnitude.

TO EXTERNAL UTiLIZATlON CIRCUITRY Mfl POTENTIAL REGULATOR ALTERNATORUNDER-FREQUENCY DETECTING CIRCUIT This invention is directed to acircuit for detecting less than normal alternator output potentialfrequencies and which reduces alternator output potential magnitude withconditions of less than normal output frequency.

With many types of prime movers, the speed of rotation of an alternatorrotor may decrease. A decrease of alternator rotor speed reduces thealternator output potential magnitude and frequency. Potential regulatorcircuits currently employed to regulate alternator output potentialmagnitude are sensitive to potential magnitude and insensitive topotential frequency. Consequently, upon a reduction of alternator outputpotential magnitude as a result of a reduction of rotor speed, thepotential regulator circuit increases the magnitude of alternator fieldexcitation to maintain the alternator output potential magnitudeconstant at the preselected value. If this condition is permitted topersist, the alternator field winding may be destroyed. Therefore, acircuit which is frequency sensitive and detects conditions of less thannormal alternator output potential frequency to reduce the alternatoroutput potential magnitude by reducing the field excitation withconditions of less than normal output potential frequency is desirable.

It is, therefore, an object of this invention to provide a frequencysensitive circuit for reducing alternator output potential magnitudewith conditions of less than normal output potential frequency.

It is another object of this invention to provide an improved alternatorunderfrequency detecting circuit for reducing the alternator outputpotential with conditions of less than normal output potentialfrequency.

In accordance with this invention, an alternator underfrequencydetecting circuit for reducing the alternator.output potential withconditions of less than normal output potential frequency is providedwherein a source of each an alternating current-sensing potential and analternating current auxiliary sensing potential are connected in seriesaiding relationship across the alternating current input circuitry of asensing potential rectifier circuit and two silicon-controlledrectifiers, which are triggered conductive only with normal alternatoroutput potential frequency, are connected in an opposite polarityrelationship across the source of auxiliary sensing potential wherebywith conditions of normal alternator output potential frequency, theauxiliary sensing potential is effectively shunted from the sensingpotential rectifier circuit by the silicon-controlled rectifiers toprovide normal operation of the alternator-regulator system and withconditions of less than normal alternator output potential frequency,the sources of sensing potential and auxiliary sensing potential areapplied in series aiding relationship across the sensing potentialrectifier circuit to decrease alternator output potential magnitude.

For a better understanding of the present invention, together withadditional objects, advantages and features thereof, reference is madeto the following description and accompanying single FIGURE drawingwhich sets forth the alternator underfrequency detecting circuit of thisinvention in schematic form.

Referring to the FIGURE, the alternator underfrequency detecting circuitof this invention for reducing the alternator output potential withconditions of less than normal output potential frequency is set forthin schematic form in combination with an alternator 8, a sensingpotential rectifier circuit, which may be a full-wave bridge typerectifier circuit having alternating current input circuitry, which maybe terminals 11 and 12, and direct current output circuitry, which maybe terminals 13 and 14, and a potential regulator circuit 15 connectedacross the rectifier circuit output circuitry and comprises a source ofeach an alternating current sensing potential, secondary winding 22 oftransformer 20, and an alternating current auxiliary sensing potential,secondary winding 23 of transformer 20, each of a frequency the same asthe frequency of the output potential of alternator 8, first and secondsilicon-controlled rectifiers 30 and 35, each having anode, cathode andgate electrodes and circuitry for producing a trigger signal at thebeginning of each selected half-cycle of the alternating currentauxiliary sensing potential for a predetermined duration of time greaterthan the normal frequency period of the selected half-cycles, which maybe a conventional monostable multivibrator circuit such as that setforth in schematic form within dashed rectangle 16.

As the potential regulator circuit may be any one of the manyconventional potential regulator circuits well known in the art and, perse, forms no part of this invention, it has been illustrated in thedrawing in block form.

The alternator 8 is illustrated in schematic form and includes threeoutput coils 8a, 8b and 8c and a field coil 9.

Field coil 9 is connected across the output terminals of potentialregulator 15 through leads l7 and 18. With this arrangement, thepotential regulator 15 is responsive to the alternator output potentialmagnitude and provides for the proper energization of field coil 9 tomaintain a substantially constant predetermined alternator outputpotential by increasing and decreasing the energization of field coil 9with decreases and increases, respectively, of the alternator outputpotential magnitude in a manner well known in the art.

One arrangement for providing a source of each an alternating currentsensing potential and an alternating current auxiliary sensingpotential, each of a frequency the same as the frequency of the outputpotential of the alternator, is by transformer coupling two secondarywindings to a selected output phase of alternator 8 such as secondarywindings 22 and 23 of transformer 20 which are magnetically coupled toprimary winding 21 connected across alternator output coils 8a and 8b.It is to be specifically understood that primary winding 21 may beconnected across any other two alternator output coils and that aseparate primary winding for each of secondary windings 22 and 23 may beemployed. For purposes of this description of the novel alternatorunderfrequency detecting circuit of this invention and without intentionor inference of a limitation thereto, it will be assumed that thepotential induced in secondary winding 22 is the alternating currentsensing potential and the potential induced secondary winding 23 is thealternating current auxiliary sensing potential.

With secondary windings 22 and 23 poled as illustrated in the soleFIGURE, terminal ends 22a and 23a of respective secondary windings 22and 23 of a positive polarity during the same half-cycles, the source ofalternating current sensing potential and the source of alternatingcurrent auxiliary sensing potential are connected in series aidingrelationship across the sensing potential rectifier circuit 10alternating current input circuitry. Over those half-cycles of thealternating current sensing and auxiliary sensing potentials duringwhich terminal ends 22a and 23a of respective secondary winding 22 and23 are of a positive polarity, these respective sources of sensing andauxiliary sensing potential are connected across the sensing potentialrectifier circuit 10 alternating current input circuitry through acircuit which may be traced from terminal end 22a of secondary winding22, through lead 24 to input terminal 11 of sensing potential rectifiercircuit 10, from input terminal 12 of sensing potential rectifiercircuit 10 through lead 25 to a potential control rheostat 26, throughlead 27, an impedance including series resistors 28 and 29, lead 34,through secondary winding 23 in a negative to a positive direction fromterminal end 23b to terminal end 23a, lead 39 and through secondarywinding 22 in a negative to a positive direction from terminal end 22bto terminal end 22a. During the other half-cycles, this circuit may betraced from positive polarity terminal end 22b of secondary winding 23,through lead 39 and secondary winding 23 in a negative to a positivedirection from terminal end 23a to a terminal end 23b, through theimpedance, the potential control rheostat of the sensing potentialrectifier circuit and through secondary winding 22 in a negative to apositive direction from terminal end 22a to terminal end 22b. Potentialcontrol rheostat 26 may be included in this circuit for selecting thedesired magnitude of alternator output potential:

The anode-cathode electrodes of silicon-controlled rectifiers 30 and 35are connected in an opposite polarity relationship across the source ofalternating current auxiliary sensing potential. The anode electrode 36of silicon-controlled rectifier 35 is connected to terminal end 23a ofsecondary winding 23 through lead 46 and the cathode electrode 37 ofsilicon-controlled rectifier 35 is connected to terminal end 23b ofsecondary winding 23 through leads &7 and 27, the impedance comprisingseries resistors 28 and 29 and lead 34. The anode electrode 31 ofsilicon-controlled rectifier 30 is connected to output terminal 23b ofsecondary winding 23 through leads 48 and 27, the impedance comprisingresistors 28 and 29 and lead 34 and the cathode electrode 32 ofsiliconcontrolled rectifier 30 is connected to output terminal 23a ofsecondary winding 23 through leads 54 and 55.

To produce a trigger signal at the beginning of each selected half-cycleof the alternating current auxiliary sensing potential for apredetermined duration of time greater than the normal frequency periodof the selected half-cycles, a conventional monostable multivibratorcircuit, such as that schematically represented within dashed rectangle16, may be employed. The operation of this circuit will be described indetail later in this specification.

To supply the direct current operating potential for the monostablemultivibrator circuit 16, the alternating current auxiliary sensingpotential may be half-wave rectified by a diode 56, the anode electrodeof which is connected to terminal end 23b of secondary winding 23through a current limiting resistor 57 and lead 53 and the cathodeelectrode of which is connected to terminal end 23a of secondary winding23 through a zener diode 60 and leads 61, 62 and S. Zener diode 60 isselected to have an inverse breakdown potential of a magnitude equal tothe rated operating potential of the transistors selected as transistors40 and 50 of the monostablemultivibrator circuit. The half-waverectified alternating current auxiliary sensing potential is filtered bycapacitor 65 and appears as a direct current potential across leads 69and 62 of a positive and a negative polarity, respectively. As therespective collector electrodes 42 and 52 of type NPN-transistors 40 and50 of monostable multivibrator circuit 16 are connected to the positivepolarity lead 69 through respective collector resistors 70 and 71 andthe respective emitter electrodes 43 and 53 are connected to thenegative polarity lead 62, these type NPN transistors are poled forforward conduction through the collector-emitter electrodes thereof.

As is well known in the art, the monostable multivibrator circuit may beswitched from the normal, stable state to an alternate state andspontaneously returns to the stable state at the conclusion of apredetermined time interval.

In the stable state of multivibrator circuit 16, transistor 40 conductsthrough the collector-emitter electrodes and transistor 50 is notconducting. Upon monostable multivibrator circuit 16 being triggered tothe alternate state in a manner to be explained in detail later in thisspecification, transistor 50 conducts through the collector-emitterelectrodes and transistor 40 is not conducting. While monostablemultivibrator 16 is in the alternate state, capacitor 80 charges throughresistor 78, variable resistor 79 and the collector-emitter electrodesof transistor 50. When capacitor 80 has become charged, the potentialupon junction 97 becomes positive and is of the proper polarity toproduce base-emitter current flow through type NPN-transistor 40. Theresulting flow of collector-emitter current flow through transistor 40triggers this device conductive through the collector-emitterelectrodes. Upon the conduction of transistor 41) through thecollectoremitter electrodes, the base electrode 51 of transistor 50 isconnected to negative polarity lead 62 through resistor 98, a conditionwhich extinguishes transistor 50 and returns monostable multivibratorcircuit 16 to the stable state. Diode 89 may be included in thebase-emitter circuit of transistor 40 to improve the temperaturestability of monostable multivibrator circuit 16.

While multivibrator circuit 16 is in the alternate state, withtransistor 40 not conducting, the potential of junction 75 is of apositive polarity with respect to lead 62. This potential, which is thetrigger signal produced by monostable multivibrator circuit 16, isapplied across the gate-cathode electrodes of the one silicon-controlledrectifier which is reverse poled by the auxiliary sensing potentialduring the selected half-cycles. For purposes of this specification, andwithout intention or inference of a limitation thereto, it will beassumed that the selected half cycles of the alternating currentauxiliary sensing potential are those half-cycles during which terminalends 230 and 23b of secondary winding 23 are of a positive and anegative polarity, respectively. The trigger signal produced bymonostable multivibrator circuit 16 while in the alternate state,therefore, is applied across the gate electrode 33 and the cathodeelectrode 32 of silicon controlled rectifier 30 through current limitingresistor 76.

The duration of time which monostable multivibrator circuit 16 is in thealternate state is determined by the time constant of the circuitincluding resistor 78, variable resistor 79 and capacitor 80.Consequently, the duration of time that monostable multivibrator circuit16 remains in the alternate state may be precisely selected by adjustingvariable resistor 79. For purposes of this specification and withoutintention or inference of a limitation thereto, it will be assumed thatthe normal output potential frequency of alternator 8 is 60 cycles persecond. For reasons which will become apparent later in thisspecification, monostable multivibrator circuit 16 must produce atrigger signal for a predetermined duration of time greater than thenormal frequency period of the selected halfcycles. Therefore,monostable multivibrator circuit 16 must remain in the alternate statefor a duration of time greater than the period of a half-cycle of a 60cycle potential dependent upon the minimum output potential frequency atwhich the novel frequency detecting circuit of this invention is desiredto become operative. For example, if it is desired that the circuit ofthis invention become operative when the frequency of alternator 8output potential has decreased below 55 cycles per second, potentiometer79 is adjusted to maintain monostable multivibrator circuit 16 in thealternate state for a period of 9.09 milliseconds, the period ofone-half cycle of a 55 cycle potential. It will be assumed for purposesof this specification that variable resistor 79 is adjusted to providefor monostable multivibrator circuit 16 to remain in the alternate statefor a duration of time of 9.09 milliseconds.

Provision is made for applying the auxiliary sensing potential acrossthe gate-cathode electrodes of the other siliconcontrolled rectifier 35during each other half-cycle of the auxiliary sensing potential whilesilicon-controlled rectifier 30 is conducting and for triggering theother silicon-controlled rectifier 35 conductive during each selectedhalf-cycle of the auxiliary sensing potential only aftersilicon-controlled rectifier 30 has conducted during the preceding otherhalf-cycle. The series combination of a diode 83, a resistor 84 and acapacitor 85 is connected across secondary winding 23 through a circuitwhich may be traced from terminal end 23b thereof through lead 34through the series combination of diode 83, resistor 84 and capacitor85, leads 27 and 48, the anode-cathode electrodes of silicon-controlledrectifier 30 and leads 54 and 55 to terminal end 23a of secondarywinding 23. The gate electrode 38 of silicon-controlled rectifier 35 isconnected to junction 86 between diode 83 and capacitor 85 through acurrent limiting resistor 87. Resistor 88 may be connected across thegate-cathode electrodes of silicon-controlled rectifier 35 to providenoise immunity. The operation of this circuitry will be explained indetail later in this specification.

Upon startup, over the first half-cycle of auxiliary sensing potentialduring which terminal end 23b of secondary winding 23 is of a positivepolarity with respect to terminal end 23a, the auxiliary sensingpotential is rectified by diode 56 and appears as a positive andnegative polarity direct current operating potential across respectiveleads 69 and 62. Consequently, monostable multivibrator l6 settles intoits stable state with transistor 40 conducting and transistor 50 notconducting.

At the beginning of the next half-cycle, a selected half-cycle, of thealternating current auxiliary supply potential, during which terminalend 23a of secondary winding 23 is of a positive polarity with respectto terminal end 23b, the monostable multivibrator circuit 16 is in thestable state, consequently, the trigger signal produced thereby is notpresent upon junction 75 and capacitor 91 charges through a circuitwhich may be traced from terminal end 230 of secondary winding 23,through leads 55 and d2, resistor 90, capacitor 91 lead 92, diode 93,and lead 9d, impedance 29 and lead 34 to terminal end 23b of secondarywinding 23. When the potential across resistor 99 and capacitor 91 hasreached a magnitude which exceeds the breakdown potential of a potentialsensitive switch 95, which may be any one of the many potentialsensitive bilateral or unilateral potential sensitive electricalswitches commercially available from the General Electric Company andMotorola Semiconductor Products, Inc., this device conducts to provide adischarge path for capacitor 91 through the base electrode 51 and theemitter electrode 53 of type NPN-transistor St) in the proper polarityrelationship to produce base-emitter current flow through a type NPNtransistor. The resulting flow of base-emitter current flow throughtransistor 50 triggers this device conductive through thecollector-emitter electrodes thereof to place junction 96 at a negativepolarity potential, a condition which extinguishes conducting transistor40 to place monostable multivibrator circuit 16 in the alternate state.Resistor 95) is of a low ohmic value, consequently, capacitor 91 chargesrapidly to trigger monostable multivibrator circuit 16 to the alternatestate substantially at the beginning of each selected half-cycle of theauxiliary sensing potential. The trigger signal produced by monostablemultivibrator 16 at this time is ineffective as silicon-controlledrectifier 30 is reverse biased by the auxiliary alternating currentsensing potential.

Assuming a normal alternator 8 output potential frequency, at thebeginning of the next half-cycle of the alternating current auxiliarysensing potential during which terminal end 23b of secondary winding 23is of a positive polarity with respect to terminal end 23a, the triggersignal produced by monostable multivibrator 16 is still present as theperiod of a half-cycle of a 60 cycle potential is 8.33 milliseconds. Assilicon-controlled rectifier 30 is forward poled during these otherhalf-cycles by the auxiliary alternating current sensing potential,which is of a magnitude greater than the alternating current sensingpotential of secondary winding 22, silicon-controlled rectifier 30 istriggered conductive through the anode-cathode electrodes. Whilesilicon-controlled rectifier 30 is conducting, capacitor 85 chargesthrough diode 83 and resistor 84. When capacitor 85 has become charged,the auxiliary sensing potential is applied across the gate-cathodeelectrodes of the other silicon-controlled rectifier 35 in the properpolarity relationship to produce gate current through this devicethrough a circuit which may be traced from terminal end 23b of secondarywinding 23, through diode 83, current limiting resistors 84 and 87, thegate-cathode electrodes of silicon-controlled rectifier 35, leads 47, 27and 48, the anode-cathode electrodes of sil-- icon-controlled rectifier30 and leads 5d and 55 to terminal end 23a of secondary winding 23. Asconducting silicon-controlled rectifier 30 effectively removes theauxiliary sensing potential from across silicon-controlled rectifier 35,this device is forward poled by the sensing potential of secondarywinding 22, consequently the gate current produced by the auxiliarysensing potential triggers this device conductive to conduct sensingcurrent through a circuit which may be traced from terminal end 22b ofsecondary winding 22, through leads 39 and 46, the anode-cathodeelectrodes of silicon-controlled rectifier 35, lead 47, potentiometer26, lead 25, through sensing potential bridge rectifier circuit and lead2d to terminal end 22a of secondary winding 22.

At the beginning of the next half-cycle, a selected half-cycle, of thealternating current auxiliary sensing potential, during which terminalend 23:: of secondary winding 23 is of a positive polarity with respectto terminal end 23b, monostable multivibrator circuit 16 is in thestable state, consequently, s'ilicon-controlled rectifier 30 does notimmediately conduct. However, charged capacitor discharges through thegate cathode electrodes of silicon-controlled rectifier 35 in the properpolarity relationship to produce gate current through this device. Assilicon-controlled rectifier 35 is now forward poled by the alternatingcurrent auxiliary sensing potential, which is of a magnitude greaterthan the alternating current sensing potential, silicon-controlledrectifier 35 conducts the current produced by the auxiliary sensingpotential through resistors 28 and 29. Concurrently, capacitor 91becomes charged through a circuit previously described until potentialsensitive switch 95 is triggered conductive to discharge capacitor 91through the base-emitter electrodes of transistor 50 to trigger themonostable multivibrator circuit 16 to the alternate state. Asconducting silicon-controlled rectifier 35 effectively removes thealternating current auxiliary sensing potential from acrosssilicon-controlled rectifier 30, the trigger signal produced bymonostable multivibrator circuit 16 triggers this device conductive toconduct sensing current through a circuit which may be traced fromterminal end 220 of secondary winding 22, through lead 24, throughbridge circuit 10, lead 25, potentiometer 26, leads 27 and 48, theanode-cathode electrodes of silicon-controlled rectifier 30 and leads54, 55 and 39 to terminal end 22b of secondary winding 22.

This action continues so long as the frequency of the output potentialof alternator 8 remains normal.

With underfrequency conditions, the monostable multivibrator circuit 16returns to its stable state before the selected half-cycle of thealternating current auxiliary sensing potential is complete.Consequently, the trigger signal for silicon-controlled rectifier 30 isnot present at the beginning of the next half-cycle to triggersilicon-controlled rectifier 30 conductive. As silicon-controlledrectifier does not conduct,

capacitor 85 does not charge and the auxiliary sensing potential is notapplied across the gate-cathode electrode of siliconcontrolled rectifier35. Consequently, neither silicon-com trolled rectifier 30 norsilicon-controlled rectifier 35 conducts. With neithersilicon-controlled rectifier conducting, the alternating current sensingpotential and the alternating current auxiliary sensing potential isconnected in series aiding relationship across the bridge circuit 10through the circuit previously described. As these potentials are inseries aiding relationship, the sensing potential to which regulator 15is responsive is increased in magnitude. In response to this increase ofsensing potential magnitude, potential regulator circuit 15 reduces theenergization of alternator field 9 to reduce the alternator 8 outputpotential. So long as the frequency of the output potential ofalternator 8 is less than normal, neither silicon controlled rectifier30 nor 35 will conduct and potential regulator 15 will operate tomaintain the output potential of alternator 8 at a reduced magnitude.

From this description of the circuit of this invention, it is apparentthat the auxiliary sensing potential is applied across the gate-cathodeelectrodes of silicon-controlled rectifier 35 during each half-cyclethereof other than the selected half-cycles while silicon-controlledrectifier 30 is conducting to complete the circuit previously describedand capacitor 85 triggers silicon-controlled rectifier 35 conductiveduring each selected half-cycle of the auxiliary sensing potential onlyafter siliconcontrolled rectifier 30 has conducted during the precedingcycle to complete the circuit, previously described, through whichcapacitor 85 is charged.

While specific electrical components and polarities have been set forthin this specification, it will be obvious to those skilled in the artthat other electrical components having similar electricalcharacteristics and compatible electrical polarities may be substitutedtherefor without departing from the spirit of the invention.

While a preferred embodiment of the present invention has been shown anddescribed, it will be obvious to those skilled in the art that variousmodifications and substitutions may be made without departing from thespirit of the invention which is to be limited only within the scope ofthe appended claims.

What is claimed is:

1. An alternator underfrequency detecting circuit for reducing thealternator output potential with conditions of less than normal outputpotential frequency comprising in combination with an alternator, asensing potential rectifier circuit having alternating current inputcircuitry and direct current output circuitry and a potential regulatorcircuit connected across the rectifier circuit output circuitry, asource of each an alternating current sensing potential and analternating current auxiliary sensing potential, each of a frequency thesame as the frequency of the output potential of said alternator, meansfor connecting said source of alternating current sensing potential andsaid source of alternating current auxiliary sensing potential in seriesaiding relationship across said sensing potential rectifier circuitalternating current input circuitry, first and second silicon-controlledrectifiers each having anode, cathode and gate electrodes, means forconnecting said anode-cathode electrodes of said silicon-controlledrectifiers in an opposite polarity relationship across said source ofalternating current auxiliary sensing potential, means for producing atrigger signal at the beginning of each selected half-cycle of saidalternating current auxiliary sensing potential for a predeterminedduration of time greater than the normal frequency period of saidselected half-cycles, means for applying said trigger signal across saidgate-cathode electrodes of the one said silicon-controlled rectifierwhich is reverse poled by said auxiliary sensing potential during saidselected half-cycles thereof, means for applying said auxiliary sensingpotential across said gate cathode electrodes of the other saidsilicon-controlled rectifier during each other half-cycle of saidauxiliary sensing potential while said the one said silicon-controlledrectifier is conducting, and means for triggering said other saidsilicon-controlled rectifier conductive during each selected half-cycleof said auxiliary sensing potential only after said the one saidsilicon-controlled rectifier has conducted during the preceding othersaid half-cycle.

2. An alternator underfrequency detecting circuit for reducing thealternator output potential with conditions of less than normal outputpotential frequency comprising in combination with an alternator, asensing potential rectifier circuit having alternating current inputcircuitry and direct current output circuitry and a potential regulatorcircuit connected across the rectifier output circuitry, a source ofeach an alternating current sensing potential and an alternating currentauxiliary sensing potential, each ofa frequency the same as thefrequency of the output potential of said alternator, an impedance,means including said impedance for connecting said source of alternatingcurrent sensing potential and said source of alternating currentauxiliary sensing potential in series aiding relationship across saidsensing potential rectifier circuit alternating current input circuitry,first and second silicon-controlled rectifiers each having anode,cathode and gate electrodes, means for connecting said anode-cathodeelectrodes of said silicon-controlled rectifiers in an opposite polarityrelationship across said source of alternating current auxiliary sensingpotential, means for producing a trigger signal at the beginning of eachselected half-cycle of said alternating current auxiliary sensingpotential for a predetermined duration of time greater than the normalfrequency period of said selected half-cycles, means for applying saidtrigger signal across said gate-cathode electrodes of the one saidsiliconcontrolled rectifier which is reverse poled by said auxiliarysensing potential during said selected half-cycles thereof, means forapplying said auxiliary sensing potential across said gate-cathodeelectrodes of the other said silicon-controlled rectifier during eachother half-cycle of said auxiliary sensing potential while said the onesaid silicon-controlled rectifier is conducting, and means fortriggering said other said siliconcontrolled rectifier conductive duringeach selected half-cycle of said auxiliary sensing potential only aftersaid the one said silicon-controlled rectifier has conducted during thepreceding other said half-cycle.

3. An alternator underfrequency detecting circuit for reducing thealternator output potential with conditions of less than normal outputpotential frequency comprising in combination with an alternator, asensing potential rectifier circuit having alternating current inputcircuitry and direct current output circuitry and a potential regulatorcircuit connected across the rectifier output circuitry, a source ofeach an alternating current sensing potential and an alternating currentauxiliary sensing potential, each of a frequency the same as thefrequency of the output potential of said alternator, an impedance,means including said impedance for connecting said source of alternatingcurrent sensing potential and said source of alternating currentauxiliary sensing potential in series aiding relationship across saidsensing potential rectifier circuit alternating current input circuitry,first and second silicon-controlled rectifiers each having anode,cathode and gate electrodes, means for connecting said anode-cathodeelectrodes of said silicon-controlled rectifiers in an opposite polarityrelationship across said source of alternating current auxiliary sensingpotential, a monostable multivibrator circuit responsive to selectedhalf-cycles of said auxiliary sensing potential, for producing a triggersignal at the beginning of each said selected half-cycle thereof for apredetermined duration of time greater than the normal frequency periodof said selected half-cycles, means for applying said trigger signalacross said gate-cathode electrodes of the one said silicon-controlledrectifier which is reverse poled by said auxiliary sensing potentialduring said selected half-cycles thereof, means for applying saidauxiliary sensing potential across said gate-cathode electrodes of theother said silicon-controlled rectifier during each other half-cycle ofsaid auxiliary sensing potential while said the one saidsilicon-controlled rectifier is conducting, and means for triggeringsaid other said silicon-controlled rectifier conductive during eachselected half-cycle of said auxiliary sensing potential only after saidthe one said silicon-controlled rectifier has conducted during thepreceding other said halfcycle.

4. An alternator underfrequency detecting circuit for reducing thealternator output potential with conditions of less than normal outputpotential frequency comprising in combination with an alternator, asensing potential rectifier circuit having alternating current inputcircuitry and direct current output circuitry and a potential regulatorcircuit connected across said rectifier output circuitry, a source ofeach an alternating current sensing potential and an alternating currentauxiliary sensing potential, each ofa frequency the same as thefrequency of the output potential of said alternator, an impedance,means including said impedance for connecting said source of alternatingcurrent sensing potential and said source of alternating currentauxiliary sensing potential in series aiding relationship across saidsensing potential rectifier circuit alternating current input circuitry,first and second silicon-controlled rectifiers each having anode,cathode and gate electrodes, means for connecting said anode-cathodeelectrodes of said silicon controlled rectifiers in an opposite polarityrelationship across said source of alternating current auxiliary sensingpotential, a monostable multivibrator circuit responsive to selectedhalf-cycles of said auxiliary sensing potential for producing a triggersignal at the beginning of each said selected halfcycle thereof for apredetermined duration of time greater than the normal frequency periodof said selected half-cycles, means for applying said trigger signalacross said gate-cathode electrodes of the one said silicon-controlledrectifier which is reverse poled by said auxiliary sensing potentialduring said selected half-cycles thereof, a diode, a capacitor, meansfor connecting said diode and said capacitor in series across saidsource of alternating current auxiliary sensing potential, and means forconnecting said gate electrode of the other said silicon-controlledrectifier to the junction between said diode and said capacitor.

5. An alternator underfrequency detecting circuit for reducing thealternator output potential with conditions of less than normal outputpotential frequency comprising in combination with an alternator, asensing potential rectifier circuit having alternating current inputcircuitry and direct current output circuitry and a potential regulatorcircuit connected across said rectifier output circuitry, a source ofeach an alternating current sensing potential and an alternating currentauxiliary sensing potential, each of a frequency the same as thefrequency of the output potential of said alternator, an impedance,means including said impedance for connecting said source of alternatingcurrent sensing potential and said source of alternating currentauxiliary sensing potential in series aiding relationship across saidsensing potential rectifier circuit alternating current input circuitry,first and second silicon-controlled rectifiers each having anode,cathode and gate electrodes, means for connecting said anode-cathodeelectrodes of said silicon-controlled rectifiers in an opposite polarityrelationship across said source of alternating current auxiliary sensingpotential, a monostable multivibrator circuit responsive to selectedhalf-cycles of said auxiliary sensing potential for producing a triggersignal at the beginning of each said selected half-cycle thereof for apredetermined duration of time greater than the normal frequency periodof said selected half-cycles, means for applying said trigger signalacross said gate-cathode electrodes of the one said silicon-controlledrectifier which is reverse poled by said auxiliary sensing potentialduring said selected half-cycles thereof, a diode, a resistor, acapacitor, means for connecting said diode, said resistor and saidcapacitor in series across said source of alternating current auxiliarysensing potential in that order, and means for connecting said gateelectrode of the other said silicon-controlled rectifier to the junctionbetween said resistor and said capacitor.

1. An alternator underfrequency detecting circuit for reducing thealternator output potential with conditions of less than normal outputpotential frequency comprising in combination with an alternator, asensing potential rectifier circuit having alternating current inputcircuitry and direct current output circuitry and a potential regulatorcircuit connected across the rectifier circuit output circuitry, asource of each an alternating current sensing potential and analternating current auxiliary sensing potential, each of a frequency thesame as the frequency of the output potential of said alternator, meansfor connecting said source of alternating current sensing potential andsaid source of alternating current auxiliary sensing potential in seriesaiding relationship across said sensing potential rectifier circuitalternating current input circuitry, first and second silicon-controlledrectifiers each having anode, cathode and gate electrodes, means forconnecting said anodecathode electrodes of said silicon-controlledrectifiers in an opposite polarity relationship across said source ofalternating current auxiliary sensing potential, means for producing atrigger signal at the beginning of each selected half-cycle of saidalternating current auxiliary sensing potential for a predeterminedduration of time greater than the normal frequency period of saidselected half-cycles, means for applying said trigger signal across saidgate-cathode electrodes of the one said silicon-controlled rectifierwhich is reverse poled by said auxiliary sensing potential during saidselected half-cycles thereof, means for applying said auxiliary sensingpotential across said gate cathode electrodes of the other saidsiliconcontrolled rectifier during each other half-cycle of saidauxiliary sensing potential while said the one said siliconcontrolledrectifier is conducting, and means for triggering said other saidsilicon-controlled rectifier conductive during each selected half-cycleof said auxiliary sensing potential only after said the one saidsilicon-controlled rectifier has conducted during the preceding othersaid half-cycle.
 2. An alternator underfrequency detecting circuit forreducing the alternator output potential with conditions of less thannormal output potential frequency comprising in combination with analternator, a sensing potential rectifier circuit having alternatingcurrent input circuitry and direct current output circuitry and apotential regulator circuit connected across the rectifier outputcircuitry, a source of each an alternating current sensing potential andan alternating current auxiliary sensing potential, each of a frequencythe same as the frequency of the output potential of said alternator, animpedance, means including said impedance for connecting said source ofalternating current sensing potential and said source of alternatingcurrent auxiliary sensing potential in series aiding relationship acrosssaid sensing potential rectifier circuit alternating current inputcircuitry, first and second silicon-controlled rectifiers each havinganode, cathode and gate electrodes, means for connecting saidanode-cathode electrodes of said silicon-controlled rectifiers in anopposite polarity relationship across said source of alternating currentauxiliary sensing potential, means for producing a trigger signal at thebegInning of each selected half-cycle of said alternating currentauxiliary sensing potential for a predetermined duration of time greaterthan the normal frequency period of said selected half-cycles, means forapplying said trigger signal across said gate-cathode electrodes of theone said silicon-controlled rectifier which is reverse poled by saidauxiliary sensing potential during said selected half-cycles thereof,means for applying said auxiliary sensing potential across saidgate-cathode electrodes of the other said silicon-controlled rectifierduring each other half-cycle of said auxiliary sensing potential whilesaid the one said silicon-controlled rectifier is conducting, and meansfor triggering said other said silicon-controlled rectifier conductiveduring each selected half-cycle of said auxiliary sensing potential onlyafter said the one said silicon-controlled rectifier has conductedduring the preceding other said half-cycle.
 3. An alternatorunderfrequency detecting circuit for reducing the alternator outputpotential with conditions of less than normal output potential frequencycomprising in combination with an alternator, a sensing potentialrectifier circuit having alternating current input circuitry and directcurrent output circuitry and a potential regulator circuit connectedacross the rectifier output circuitry, a source of each an alternatingcurrent sensing potential and an alternating current auxiliary sensingpotential, each of a frequency the same as the frequency of the outputpotential of said alternator, an impedance, means including saidimpedance for connecting said source of alternating current sensingpotential and said source of alternating current auxiliary sensingpotential in series aiding relationship across said sensing potentialrectifier circuit alternating current input circuitry, first and secondsilicon-controlled rectifiers each having anode, cathode and gateelectrodes, means for connecting said anode-cathode electrodes of saidsilicon-controlled rectifiers in an opposite polarity relationshipacross said source of alternating current auxiliary sensing potential, amonostable multivibrator circuit responsive to selected half-cycles ofsaid auxiliary sensing potential, for producing a trigger signal at thebeginning of each said selected half-cycle thereof for a predeterminedduration of time greater than the normal frequency period of saidselected half-cycles, means for applying said trigger signal across saidgate-cathode electrodes of the one said silicon-controlled rectifierwhich is reverse poled by said auxiliary sensing potential during saidselected half-cycles thereof, means for applying said auxiliary sensingpotential across said gate-cathode electrodes of the other saidsilicon-controlled rectifier during each other half-cycle of saidauxiliary sensing potential while said the one said silicon-controlledrectifier is conducting, and means for triggering said other saidsilicon-controlled rectifier conductive during each selected half-cycleof said auxiliary sensing potential only after said the one saidsilicon-controlled rectifier has conducted during the preceding othersaid half-cycle.
 4. An alternator underfrequency detecting circuit forreducing the alternator output potential with conditions of less thannormal output potential frequency comprising in combination with analternator, a sensing potential rectifier circuit having alternatingcurrent input circuitry and direct current output circuitry and apotential regulator circuit connected across said rectifier outputcircuitry, a source of each an alternating current sensing potential andan alternating current auxiliary sensing potential, each of a frequencythe same as the frequency of the output potential of said alternator, animpedance, means including said impedance for connecting said source ofalternating current sensing potential and said source of alternatingcurrent auxiliary sensing potential in series aiding relationship acrosssaid sensing potenTial rectifier circuit alternating current inputcircuitry, first and second silicon-controlled rectifiers each havinganode, cathode and gate electrodes, means for connecting saidanode-cathode electrodes of said silicon-controlled rectifiers in anopposite polarity relationship across said source of alternating currentauxiliary sensing potential, a monostable multivibrator circuitresponsive to selected half-cycles of said auxiliary sensing potentialfor producing a trigger signal at the beginning of each said selectedhalf-cycle thereof for a predetermined duration of time greater than thenormal frequency period of said selected half-cycles, means for applyingsaid trigger signal across said gate-cathode electrodes of the one saidsilicon-controlled rectifier which is reverse poled by said auxiliarysensing potential during said selected half-cycles thereof, a diode, acapacitor, means for connecting said diode and said capacitor in seriesacross said source of alternating current auxiliary sensing potential,and means for connecting said gate electrode of the other saidsilicon-controlled rectifier to the junction between said diode and saidcapacitor.
 5. An alternator underfrequency detecting circuit forreducing the alternator output potential with conditions of less thannormal output potential frequency comprising in combination with analternator, a sensing potential rectifier circuit having alternatingcurrent input circuitry and direct current output circuitry and apotential regulator circuit connected across said rectifier outputcircuitry, a source of each an alternating current sensing potential andan alternating current auxiliary sensing potential, each of a frequencythe same as the frequency of the output potential of said alternator, animpedance, means including said impedance for connecting said source ofalternating current sensing potential and said source of alternatingcurrent auxiliary sensing potential in series aiding relationship acrosssaid sensing potential rectifier circuit alternating current inputcircuitry, first and second silicon-controlled rectifiers each havinganode, cathode and gate electrodes, means for connecting saidanode-cathode electrodes of said silicon-controlled rectifiers in anopposite polarity relationship across said source of alternating currentauxiliary sensing potential, a monostable multivibrator circuitresponsive to selected half-cycles of said auxiliary sensing potentialfor producing a trigger signal at the beginning of each said selectedhalf-cycle thereof for a predetermined duration of time greater than thenormal frequency period of said selected half-cycles, means for applyingsaid trigger signal across said gate-cathode electrodes of the one saidsilicon-controlled rectifier which is reverse poled by said auxiliarysensing potential during said selected half-cycles thereof, a diode, aresistor, a capacitor, means for connecting said diode, said resistorand said capacitor in series across said source of alternating currentauxiliary sensing potential in that order, and means for connecting saidgate electrode of the other said silicon-controlled rectifier to thejunction between said resistor and said capacitor.